HarmonyOS Tabs 官方示例9，支持在BarMode.Fixed下，下划线支持动画移动到点击的tab下。但是没有支持BarMode.Scrollable模式下，下划线动画移动交互

import curves from '@ohos.curves';
import display from '@ohos.display';
import { BusinessError } from '@ohos.base';
import componentUtils from '@ohos.ArkUI.componentUtils';


class MyDataSource implements IDataSource {
  private list: number[] = []

  constructor(list: number[]) {
    this.list = list
  }

  totalCount(): number {
    return this.list.length
  }

  getData(index: number): number {
    return this.list[index]
  }

  registerDataChangeListener(listener: DataChangeListener): void {
  }

  unregisterDataChangeListener() {
  }
}

@Entry
@Component
struct swiperTab {
  private displayInfo: display.Display | null = null;
  private controller: TabsController = new TabsController()
  private data: MyDataSource = new MyDataSource([]);
  private initialTabMargin: number = 5; //初始化时tabbarmargin
  private animationDuration: number = 300; //动画时间
  private animationCurve: ICurve = curves.interpolatingSpring(7, 1, 328, 34); //动画曲线
  @State currentIndex: number = 0; //内容区当前Index
  @State tabsWidth: number = 0; // vp 内容区宽度
  @State indicatorWidth: number = 0; // vp 页签宽度
  @State indicatorMarginLeft: number = 5; // vp 当前页签距离左边margin
  @State indicatorIndex: number = 0; //当前页签Index
  @State nextIndicatorIndex: number = 0; //下一个目标页签Index
  @State swipeRatio: number = 0; //判断是否翻页，页面滑动超过一半，tabBar切换到下一页。
  private scroller: Scroller = new Scroller();
  private arr: string[] = ['关注', '推荐', '热点', '上海', '视频', '新时代', '新歌', '新碟', '新片'];
  private textLength: number[] = [2, 2, 2, 2, 2, 3, 2, 2, 2] // 控制页签所在父容器宽度，避免造成下划线目标位置计算错误

  aboutToAppear(): void {
    this.displayInfo = display.getDefaultDisplaySync(); //获取屏幕实例
    let list: number[] = [];
    for (let i = 1; i <= this.arr.length; i++) {
      list.push(i);
    }
    this.data = new MyDataSource(list)
  }

  // 获取屏幕宽度，单位vp
  private getDisplayWidth(): number {
    return this.displayInfo != null ? px2vp(this.displayInfo.width) : 0;
  }

  // 获取组件大小、位置、平移缩放旋转及仿射矩阵属性信息。
  private getTextInfo(index: number): Record<string, number> {
    let modePosition: componentUtils.ComponentInfo = componentUtils.getRectangleById(index.toString());
    try {
      return { 'left': px2vp(modePosition.windowOffset.x), 'width': px2vp(modePosition.size.width) }
    } catch (error) {
      return { 'left': 0, 'width': 0 }
    }
  }

  // 当前下划线动画
  private getCurrentIndicatorInfo(index: number, event: SwiperAnimationEvent): Record<string, number> {
    let nextIndex = index;
    // 滑动范围限制，Swiper不可循环，Scroll保持不可循环
    if (index > 0 && event.currentOffset > 0) {
      nextIndex--; // 左滑
    } else if (index < this.data.totalCount() - 1 && event.currentOffset < 0) {
      nextIndex++; // 右滑
    }
    this.nextIndicatorIndex = nextIndex;
    // 获取当前tabbar的属性信息
    let indexInfo = this.getTextInfo(index);
    // 获取目标tabbar的属性信息
    let nextIndexInfo = this.getTextInfo(nextIndex);
    // 滑动页面超过一半时页面切换
    this.swipeRatio = Math.abs(event.currentOffset / this.tabsWidth);
    let currentIndex = this.swipeRatio > 0.5 ? nextIndex : index; // 页面滑动超过一半，tabBar切换到下一页。
    let currentLeft = indexInfo.left + (nextIndexInfo.left - indexInfo.left) * this.swipeRatio;
    let currentWidth = indexInfo.width + (nextIndexInfo.width - indexInfo.width) * this.swipeRatio;
    this.indicatorIndex = currentIndex;
    return { 'index': currentIndex, 'left': currentLeft, 'width': currentWidth };
  }

  private scrollIntoView(currentIndex: number): void {
    const indexInfo = this.getTextInfo(currentIndex);
    let tabPositionLeft = indexInfo.left;
    let tabWidth = indexInfo.width;
    // 获取屏幕宽度，单位vp
    const screenWidth = this.getDisplayWidth();
    const currentOffsetX: number = this.scroller.currentOffset().xOffset; //当前滚动的偏移量
    this.scroller.scrollTo({
      // 将tabbar可滑动时候定位在正中间
      xOffset: currentOffsetX + tabPositionLeft - screenWidth / 2 + tabWidth / 2,
      yOffset: 0,
      animation: {
        duration: this.animationDuration,
        curve: this.animationCurve, // 动画曲线
      }
    });
    this.underlineScrollAuto(this.animationDuration, currentIndex);
  }

  private startAnimateTo(duration: number, marginLeft: number, width: number): void {
    animateTo({
      duration: duration, // 动画时长
      curve: this.animationCurve, // 动画曲线
      onFinish: () => {
        console.info('play end')
      }
    }, () => {
      this.indicatorMarginLeft = marginLeft;
      this.indicatorWidth = width;
    })
  }

  // 下划线动画
  private underlineScrollAuto(duration: number, index: number): void {
    let indexInfo = this.getTextInfo(index);
    this.startAnimateTo(duration, indexInfo.left, indexInfo.width);
  }

  getStringFromResource(source: Resource): string {
    try {
      getContext(this).resourceManager.getStringSync(source.id);
      let str = getContext(this).resourceManager.getStringSync(source.id);
      return str
    } catch (error) {
      let code = (error as BusinessError).code;
      let message = (error as BusinessError).message;
      console.error(`getStringSync failed, error code: ${code}, message: ${message}.`);
      return ''
    }
  }

  build() {
    Column() {
      // tabbar
      Row() {
        Column() {
          Scroll() {
            Column() {
              Scroll(this.scroller) {
                Row() {
                  ForEach(this.arr, (item: string, index: number) => {
                    Column() {
                      Text(item)
                        .fontSize(16)
                        .borderRadius(5)
                        .fontColor(this.indicatorIndex === index ? Color.Red : Color.Black)
                        .fontWeight(this.indicatorIndex === index ? FontWeight.Bold : FontWeight.Normal)
                        .margin({ left: this.initialTabMargin, right: this.initialTabMargin })
                        .id(index.toString())
                        .onAreaChange((oldValue: Area, newValue: Area) => {
                          if (this.indicatorIndex === index &&
                            (this.indicatorMarginLeft === 0 || this.indicatorWidth === 0)) {
                            if (newValue.globalPosition.x != undefined) {
                              let positionX = Number.parseFloat(newValue.globalPosition.x.toString());
                              this.indicatorMarginLeft = Number.isNaN(positionX) ? 0 : positionX;
                            }
                            let width = Number.parseFloat(newValue.width.toString());
                            this.indicatorWidth = Number.isNaN(width) ? 0 : width;
                          }
                        })
                        .onClick(() => {
                          this.indicatorIndex = index;
                          // 点击tabbar下划线动效
                          this.underlineScrollAuto(this.animationDuration, index);
                          this.scrollIntoView(index);
                          // 跟tabs进行联动
                          this.controller.changeIndex(index)
                        })
                    }
                    .width(this.textLength[index] * 28)
                  }, (item: string) => item)
                }
                .height(32)
              }
              .width('100%')
              .scrollable(ScrollDirection.Horizontal)
              .scrollBar(BarState.Off)
              .edgeEffect(EdgeEffect.None)
              // 滚动事件回调, 返回滚动时水平、竖直方向偏移量
              .onScroll((xOffset: number, yOffset: number) => {
                console.info(xOffset + ' ' + yOffset)
                this.indicatorMarginLeft -= xOffset;
              })
              // 滚动停止事件回调
              .onScrollStop(() => {
                console.info('Scroll Stop')
                this.underlineScrollAuto(0, this.indicatorIndex);
              })

              Column()
                .width(this.indicatorWidth)
                .height(2)
                .borderRadius(2)
                .backgroundColor(Color.Red)
                .alignSelf(ItemAlign.Start)
                .margin({ left: this.indicatorMarginLeft, top: 5 })
            }
          }
        }
        .width('100%')
        .margin({ top: 15, bottom: 10 })

      }

      Tabs({ controller: this.controller }) {
        LazyForEach(this.data, (item: number, index: number) => {
          TabContent() {
            List({ space: 10 }) {
              ListItem() {
                Text(item.toString())
              }
            }
            .padding({ left: 10, right: 10 })
            .width("100%")
            .height('95%')
          }
          .onAreaChange((oldValue: Area, newValue: Area) => {
            let width = Number.parseFloat(newValue.width.toString());
            this.tabsWidth = Number.isNaN(width) ? 0 : width;
          })
        }, (item: string) => item)
      }
      .onChange((index: number) => {
        this.currentIndex = index;
      })

      .onAnimationStart((index: number, targetIndex: number, event: TabsAnimationEvent) => {
        // 切换动画开始时触发该回调。下划线跟着页面一起滑动，同时宽度渐变。
        this.indicatorIndex = targetIndex;
        this.underlineScrollAuto(this.animationDuration, targetIndex);
      })
      .onAnimationEnd((index: number, event: TabsAnimationEvent) => {
        // 切换动画结束时触发该回调。下划线动画停止。
        let currentIndicatorInfo = this.getCurrentIndicatorInfo(index, event);
        this.startAnimateTo(0, currentIndicatorInfo.left, currentIndicatorInfo.width);
        this.scrollIntoView(index);
      })
      .onGestureSwipe((index: number, event: TabsAnimationEvent) => {
        // 在页面跟手滑动过程中，逐帧触发该回调。
        let currentIndicatorInfo = this.getCurrentIndicatorInfo(index, event);
        this.indicatorIndex = currentIndicatorInfo.index; //当前页签index
        this.indicatorMarginLeft = currentIndicatorInfo.left; //当前页签距离左边margin
        this.indicatorWidth = currentIndicatorInfo.width; //当前页签宽度
      })
    }
    .width('100%')
  }
}